Thermal switching of the electrical conductivity of Si(111)(√3 x √3)Ag due to a surface phase transition

The temperature-dependent surface conductivity of the Si(111)(root 3 x root 3) Ag surface was measured using a microscopic four-point probe. The conductivity was found to undergo a sharp increase of about three orders of magnitude when the system was heated above about 220 K. This strong conductivity change is reversible and attributed to the phase transition which is generally believed to occur on this surface. It is also shown that, in order to find the true surface conductivity, it is necessary to separate it from the contribution of the bulk and space charge layer. In this work, this is achieved by using a finite-element model. A percolating network of Ag islands on Si( 111) was also studied and a much simpler behaviour (compared to that of Si(111)(root 3 x root 3) Ag) was found. The temperature-dependent conductivity of this system was found to display typical metallic behaviour. The absolute value of the conductivity is comparable to the value expected by modelling the Ag film as exhibiting the bulk Ag transport properties.